Mobile communication system with moving base station

ABSTRACT

A mobile communication system employs moving base stations moving in the direction of flow of traffic moving along a roadway. The moving base station communicates with fixed radio ports connected to a gateway office. A plurality of moving base stations are spaced apart on a closed loop and move with the flow of traffic along one roadway on one leg of the loop and with a flow of traffic on another roadway in another leg of the loop. The moving base stations communicate with a plurality of fixed radio ports connected by a signal transmission link to a gateway office which, in turn, is connected to the wire line network. The moving base stations are each provided with a pair of directional antennas with one antenna directed toward the flow of traffic and another antenna directed to the fixed radio ports.

RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 13/895,621 filed onMay 16, 2013, now U.S. Pat. No. 8,718,543; which is a continuation ofU.S. application Ser. No. 13/154,944 filed on Jun. 7, 2011, now U.S.Pat. No. 8,463,177; which is a continuation of U.S. application Ser. No.12/908,181 filed on Oct. 20, 2010, now U.S. Pat. No. 7,979,023; which isa continuation of U.S. application Ser. No. 11/733,069 filed on Apr. 9,2007, now U.S. Pat. No. 7,848,701 which is a continuation of U.S.application Ser. No. 09/401,584 filed on Sep. 22, 1999, now U.S. Pat.No. 7,221,904 which is a continuation of U.S. application Ser. No.08/953,962 filed on Oct. 20, 1997, now U.S. Pat. No. 6,026,277 which isa continuation of U.S. application Ser. No. 08/687,722 filed Jul. 26,1996, now U.S. Pat. No. 5,729,826 which is a continuation ofPCT/US95/07037, filed Jun. 2, 1995 which are all incorporated byreference in their entirety, herein.

TECHNICAL FIELD

The invention relates to cellular telephone systems in which a mobileunit communicates by wireless communication to a base station connectedto the wire telephone network and more particularly to cellulartelephone systems adapted for use with fast-moving mobile units.

BACKGROUND

In a typical cellular telephone system, an area is divided into aplurality of cells with each cell having a centrally located cell site.A mobile unit moving in such a cellular network communicates by radiowith a nearest cell site. The cell sites are each connected by cable orpoint-to-point microwave to a telephone network interface. The networkinterface typically provides communication among cell sites and betweenthe cell sites and the so-called wire line telephone network. Thefunctions of a typical network interface are described in The BellSystem Technical Journal, January 1979, Volume 58, No. 1. One of thefunctions to be performed by the telephone network interface is theso-called “handoff” function. As a mobile unit moves through a cellularnetwork, it will move away from one cell site and toward another cellsite. Each cell site monitors signal quality of the signal received fromthe mobile unit and passes information to the telephone networkinterface and determines when a call in progress is to be transferredfrom one cell site to another. This procedure is known as “handoff”. Thehandoff process involves several operations including selecting a cellsite trunk between the MTSO and the new cell site, sending a message tothe mobile unit transmitter/receiver to tune from its present voicechannel to a voice channel in the new cell site corresponding to thenewly selected trunk, setting up a talking path in the MTSO from thecell site trunk to the trunk of the telephone network presently in usein the call, and idling the talking path in the switching network in theMTSO between the old cell trunk and the telephone network trunk assignedto the call.

A problem with existing mobile telephone systems is the considerabletime required in handoffs. This becomes a particular problem in urbanareas which are highly congested. A basic principle of cellulartelephone systems is the concept of frequency reuse. It can be shownthat traffic capacity of a cellular system is increased by a factorN.sup.2 as the size of the cell, i.e., its diameter, is decreased by afactor of N. This is due to the fact that, at least in principle, allfrequencies in the mobile telephone spectrum are available for use ineach independent cell. Thus, as the number of cells is increased, thetotal number of calls that can concurrently exist in an area isincreased. A drawback, however, to decreasing the size of the cells isthat a mobile unit tends to cross cell boundaries more often, requiringa larger number of handoffs which will tend to overload the mobiletelephone switching office (MTSO) to the point where existing calls maybe interrupted or dropped.

Personal communication service (PCS) functions in substantially the samemanner as the mobile cellular system. In PCS, the user may be in abuilding or walking in a street or riding a vehicle and using a handsetwhich communicates with a base station in the same manner that themobile unit communicates with the base station or cell site in thecellular network. It is envisioned that PCS, by implementing very smallcells, could provide service to a very large number of users, forexample in a densely populated urban area. The difficulty with PCS isthe same as in the cellular system in that handoffs become thebottleneck.

Modern cellular systems use what is known as code division multipleaccess (CDMA) spread-spectrum communications. In direct-sequence codingCDMA (DS-CDMA), the energy of the user signal is distributed uniformlyover the system bandwidth through the spreading process providingseparation between users of the same frequency in adjacent cells. Arequirement of DS-CDMA is that no interfering signal received may besignificantly stronger than the desired signal since it would jam theweaker signal. This type of coding is used in what is sometimes referredto as hierarchal cell structures. The most commonly referencedhierarchal structure is a macro/umbrella cell overlaying a number ofmicro cells. A fast-moving mobile unit, for example, may be served bythe macro cell to avoid an extreme number of handovers. Slow-movingusers are allocated to micro cells to save capacity for the macro cells.Using the DS-CDMA concept, micro cells and macro cells share the samefrequency. To avoid strong interference at a micro cell from mobile unitin communication with a macro base station, the output power of themobile unit in the micro cell is increased to overpower the interferingsignal. The use of hierarchal cell structure to provide high-qualityspeech, data communication at rates up to 2 megabits per second andvideo communication with mobile units traveling at rates in excess of100 miles per hour and accommodating PCS are seen as needed to meetfuture mobile telecommunication demands.

In the hierarchal cell structure, the low tier, small cells, e.g., onthe order of 100 feet in diameter, accommodate low speeds. The low speedis mostly pedestrian traffic and other traffic moving at speeds below 30miles per hour. The advantages of small cells include low power, simple,inexpensive and light-weight terminals. What is desirable is an infrastructure which allows use of such terminals in all applications,whether in the home or office as a cordless phone, on streets, inshopping malls, airports, etc., and in cars on expressways at highwayspeeds. Additionally, high-spectrum reuse is needed to provide low-cost,high-quality service which requires a large bandwidth for eachsubscriber.

To provide wire line toll, quality-voice service, a 32-kilobit persecond bit rate is required with ADPCM coders. As wireless data servicesemerge, even more spectrum bandwidth will be required. In the future, itmay be possible to utilize the spectrum in the 60 gigahertz rangeproviding very large amounts of bandwidth. However, the radio wavecharacteristics at that frequency dictate a very short range, line ofsite propagation, requiring very small cells. However, as noted, smallcells and fast-moving mobile units are incompatible due to the timerequired for handoff.

SUMMARY

These and other problems of the prior art are overcome in accordancewith this invention by means of a moving base station which isinterposed between a moving mobile telephone unit and a fixed basestation. In accordance with this invention, a movable base station moveswith the traffic at a rate of speed which is comparable to the speed ofthe traffic and communicates with a moving mobile telephone unit viastandard mobile radio transmission. The movable base station furthercommunicates by radio signals with a plurality of fixed antennas spacedalong the path of travel of the mobile base station. The several fixedantennas are connected to a telephone wire line network via a telephonegateway office in a standard fashion. In accordance with this invention,the fixed radio ports are synchronized and the interface between themoving base station and the fixed radio ports is a time divisionmultiplexed (TDM)—direct-sequence, spread-spectrum CDMA.

In one particular embodiment, a number of fixed base stations areprovided in addition to moving base stations allowing slower movingtraffic, such as pedestrian traffic or rush hour mobile traffic tocommunicate via the fixed base stations.

In a specific embodiment of the invention, the moving base stations areprovided with highly directional antennas directed to moving traffic andhighly directional antennas directed to the radio ports. Communicationsfrom the fixed radio ports to the movable base stations are at arelatively low power level and from the movable base stations to themobile units are at a relatively higher power level. Due to thecharacteristics of the direct-sequence, spread-spectrum CDMA, the higherpower level signal will overpower the lower level signal such that themobile unit does not receive communications from the fixed radio portbut only from the movable base station. In the reverse direction, a lowlevel of signal is transmitted from the mobile units to the movable basestation and a high-level signal is transmitted from the base station tothe fixed radio ports, thereby eliminating any direct communication fromthe mobile unit to the fixed radio port.

In one embodiment of the invention, the movable base stations aresupported on a series of closed loops and ends of adjacent loops overlapto facilitate transfer of telephone cells between adjacent loops.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram representation of a roadway structure withfixed base stations, moving base stations, and fixed radio ports.

FIG. 2 is a block diagram representation of a fixed radio port of FIG.1.

FIG. 3 is a block diagram representation of a fixed base station of FIG.1.

FIG. 4 is a block diagram representation of a moving base station ofFIG. 1.

FIG. 5 is a block diagram representation of a gateway telephone officeshown in FIG. 1.

FIG. 6 is a tabular representation of channel allocation.

FIG. 7 is a representation of selected channels of FIG. 6.

FIG. 8 illustrates signal transmission among the various systementities.

FIG. 9 is a block diagram representation of moving base stationsoperating in separate loops.

DETAILED DESCRIPTION

FIG. 1 is a diagrammatic representation of a mobile telecommunicationsystem in accordance with one embodiment of the invention. FIG. 1represents, for example, a divided highway with mobile units 20traveling on a first roadway 10 in one direction and a plurality ofmobile units 25 traveling along a second roadway 15, in the oppositedirection. A plurality of moving base stations 30 is disposed along oneside of the roadway 10. The base stations are spaced apart by a selecteddistance equivalent to the diameter of the cell served by the movingbase station. The moving base stations 30 may be moved by means of arail 35, or other suitable conveying device which may include anautomotive vehicle traveling on the roadway, in the same direction asthe traffic flow on the roadway 10, as indicated by the arrow 12. In asimilar fashion, a plurality of moving base stations 40 are disposedadjacent the roadway 15 moving in the direction of the traffic asindicated by the arrow 17. The moving base stations 40 are moved along arail 45. The moving base stations 30, 40 may be supported on anysuitable conveying device such as rails 35, 45. The conveying device maybe at ground level or overhead, depending on the terrain and availablespace for the device. The moving base stations are preferably disposedfor optimum radio communication with the mobile units on the roadways.

Disposed between the moving base stations moving along the rails 35, 45are a plurality of fixed radio ports 50 which are connected by means ofa fiber optic ring 55 or a similar signal transmitting device to atelephone office connected to the wire line telephone network andreferred to as a gateway office. The gateway office 60 forms theinterface between the mobile telecommunication system and the wire linetelephone network. The gateway office is a well-known equipment. It ispart of the telephone network and is responsible for call processing inconjunction with the base stations. As described further later herein,the gateway office will include certain processor hardware and softwareto detect a best signal quality indication and to selectively transmitinformation with a best signal quality indicator to the telephonenetwork. A plurality of fixed base stations 70 are disposed in thevicinity of the roadway 10 and are connected to the gateway office 60 bymeans of a fiber optic ring 75 or similar signal transmission device.

In operation, the moving base stations 30 may move in the direction ofthe flow of the traffic at a rate of, for example, 60 miles per hour,which may be faster than some traffic and slower than other traffic. Themoving base station preferably handles telecommunications with mobileunits which travel at a rate of not more than 30 miles per hour fasteror slower than the moving base station. For example, the moving basestations 30, 40 may be traveling at the rate of 60 miles per hour toaccommodate traffic moving in the range of 30 to 90 miles per hour. Inthe arrangement of FIG. 1, fixed base stations 70 would accommodatecommunications with mobile units traveling at a speed of less than 30miles per hour including pedestrian traffic and stationary units. Itwill be readily apparent that instead of having fixed and moving basestations as depicted in FIG. 1, slowly moving and rapidly moving unitsmay be used as well. A particular moving base station is effective whenthe mobile units are moving in the same direction as a base station.FIG. 1 shows two roadways traveling in opposite directions with themoving base stations disposed between moving in the direction of thetraffic. The base stations may also be placed on opposite sides of thesame roadway with two-way traffic with the moving base stations movingin opposite directions on the opposite sides of the roadway.

In the typical cellular telephone system, the base station, alsoreferred to as a cell site, forms an interface between the mobile unitand the gateway office. As such, the base stations may perform a numberof functions, including functions such as locating a particular mobileunit, as well as voice processing and functions associated with callsetup, call supervision, and call termination. Additionally, the basestations typically perform the function of handing off and receiving anexisting call involving a mobile unit which has moved into or out of thenormal service area of a base station. All of these are well-known basestation functions. In some proposed mobile telephone systems, the basestations are primarily only radio interface units and a base stationcontroller, connected to a plurality of base stations performscall-handling functions for the plurality of base stations. The systemin accordance with the invention differs from the prior art primarily inthat the base stations 30, 40 are moving with the traffic andcommunicate with the gateway office 60 via fixed radio ports 50.Furthermore, in the examples described herein, the various call-handlingfunctions, including handoff, are performed by the moving base station.Advantageously, because of movement of the base station in the samedirection as the traveling mobile unit, the number of handoffs isgreatly reduced.

Each of the moving base stations 30, 40 is provided with antennas 100,101. Examples of suitable antennas for use as the antennas 100, 101,include high gain, directional antennas for use in mobile communication,and are well know and commercially available. For the example, the fixedbase stations 70 are provided with four separate antennas 110 extendingin four different directions. The antennas 100 on the base stations 30,40 are used to communicate with the mobile units 20, 25 whereas theantennas 101 on the moving base stations 30, 40 are used to communicatewith the fixed radio ports 50. The fixed base stations 70 are preferablyeach provided with four antennas 102-105. Fewer than four antennas mayalso be used. In such a case, at least one omni-directional antenna maybe used. In the exemplary configuration of FIG. 1, the antennas 102 arearranged to communicate with the mobile units 20 and the antennas103-105 are arranged to communicate with other mobile telephonecommunications from slow moving traffic or stationary subscribers. Thefixed radio ports 50, in the exemplary configuration of FIG. 1, are eachprovided with a pair of directional antennas 110, 111 of the samegeneral type as the directional antennas 100-105. As the moving basestations 30, 40 move relative to the fixed radio ports 50, datarepresenting voice signals and call related information is transmittedbetween the antennas 101 on the moving base stations 30, 40 and theantennas 110, 111 on the fixed radio ports 50.

FIG. 2 is a diagrammatic representation of an example of fixed radioports 50. In some implementations, the unit includes a standardmicroprocessor 150 as well as a radio interface circuit 154 providing aninterface between the radio signals received on the antennas 110, 111and the processor 150. For the example, the circuits are of a typetypically used in fixed base stations and are well known in the art.Additionally, each radio port 50 includes a processor 150 connected toan add/drop multiplexer (ADM) 152 in the example discussed herein. TheADM 152 interfaces with the fiber optic cable 55 and is able to add datafrom the processor 150 to the data stream on the fiber optic cable 55.Additionally, the ADM 152 recognizes a data stream accompanied by anaddress identifying the processor 150 and transfers such data from thedata stream of the fiber optic cable 55 to the processor 150. As will bedescribed further later herein, the processor 150 computes a signalquality indicator for the information received from the radio interfacecircuits 154, based primarily on radio signal strength intensity, in awell-known fashion. Processor 150 controls the transfer informationbetween the fiber optic cable 55 and the various moving base stationsvia the antennas 110, 111.

FIG. 3 is a block diagram representation of an example of one of thefixed base stations 70. The fixed base stations 70 perform the functionsof a standard prior art fixed base stations in the examples. The basestations 70 are connected to the fiber optic ring 75 and include anadd/drop multiplexer (ADM) 162 which provides an interface between theprocessor 160 and the fiber optic ring 75.

As mentioned earlier, both the optical ring 55 and optical ring 75 areconnected to the gateway office 60. The primary function of the gatewayoffice is to provide the interface to a wired telephone network. Itdistributes the telecommunications traffic between the network and themoving base stations via the fixed radio ports. The fiber optic rings55, 75 are preferably continuous rings with an add/drop multiplexer foreach ring in the gateway office. Data transmission on the fiber opticrings 55, 75 is preferably in accordance with one of the well-knownSONET or synchronous digital hierarchy (SDH) transmission protocols.

The directional antennas 100-105, 110, 111 may be of a sectorizedarchitecture or may be phased array antennas with highly directionalradio frequency beams. Such antennas are preferably used to decreaseinterference between the mobile base stations and the fixed radio ports,allowing greater spectrum reuse. Antenna diversity can be provided withtwo spatially separated radio beams separated in time with a predefinedtime-delay offset for easier separation at reception. Various techniquesfor obtaining high antenna diversity are well known in the art andantennas employing such techniques are commercially available. Othertypes of antennas may be used depending on the particularimplementation.

FIG. 4 is a block diagram representation of an example of a moving basestation 30. The station 30 includes a processor 130 connected via radiointerfaces 132, 134 to the antennas 100, 101, respectively. Theprocessor 130 may be a standard microprocessor and the radio interfacecircuits 132 may be standard radio interface circuits. Themicroprocessor is preferably programmed to handle the call processingfunctions performed in a prior art system by a cell site or by a sharedbase station controller. In this manner, the moving base station hasgreater autonomy and requires less communications with a shared basestation controller or the like. As mentioned above, however, the basestations may be primarily only radio interface units and call processingmay be performed by other equipment. The circuits 132, like the radiointerface circuits 154 in the fixed radio port 50 and the radiointerface circuits 164 in the fixed base station 70, are well known andcommercially available circuits.

For the examples herein, the radio interface between the mobile units20, 25 and the moving base stations 30, 40 and the fixed base station 70is a standard radio interface, well known in the art. The radiointerface between the moving base stations 30, 40 and the fixed radioports 50 is preferably a time division multiplexed, direct-sequence,spread-spectrum, code-division multiple-access interface (TDM/CDMA).Multiple channels between the base station and the fixed radio ports aretime division multiplexed as time slots in a data stream in theexemplary embodiments. The data stream is spread with a pseudo-randomcode over the allocated spectrum. A pilot sequence is inserted in thetransmitted signal for ease of synchronization in a well-known manner.The interface between the movable base station and the fixed radio portis preferably transparent to the overall system in spectrum use.

Frequency division or time division may be used for duplexcommunications. In the frequency division duplex (FDD) mode, data issimultaneously transmitted in both directions, each in a differentspectrum band. In a typical system in the FDD mode, the TDM frametransmission duration will be approximately 500 microseconds making theinterface substantially transparent to overall system delay.

The interface between the mobile unit and the movable base may be thestandard IS-95-based PCS air interface standard. The channel capacityfor the so-called “extended mode” (2.5 mhz) has been determined to beseven channels at 32 kilobits per second. The FCC allocated licensedspectrum for personal communications services (PCS) includes 10-mhzlicenses and 30-mhz licenses. Each 10-mhz license provides two separated5-mhz bands and each 30-mhz license provides two separated 15-mhz bands,for two-way communications. Two 5-mhz bands can support 14 duplexchannels at 32 kilobits per second and two 15-mhz bands can support 42duplex channels at 32 kilobits per second.

Voice signals between a mobile unit and the gateway office are encodedin a standard fashion using ADPCM voice encoding with a minimum bit rateof 32 kilobits per second in each channel. The interface between themoving base station and the fixed radio port is adapted to carry up to19 channels of 32 kilobits per second each at 16 bits per time slot. Theframe structure includes 16 bearer channels of 32 kilobits per second at16 bits per time slot. The time division multiplexed frame rate betweenthe movable base station and the fixed radio port is 608 kilobits persecond. To achieve a processing gain of 9 decibels, the frame rate ismultiplied by a factor of 8, yielding 4,864 kilobits per second, whichfit into a single 5-mhz band. FIG. 6 is a tabular representation of thechannel allocation showing 16 bearer channels plus 3 channels forsignaling, control, and error code. FIG. 7 is a representation ofchannels 18 and 19 of FIG. 6.

The moving base stations are addressed using predefined code sequencesderived in a known manner by the use of Walsh functions. U.S. Pat. No.5,103,459 entitled “System and Method for Generating Signal Wave Formsin CDMA Cellular Telephone System” describes the use of Walsh functionsfor code generation. U.S. Pat. No. 5,103,459 is incorporated byreference herein. As described in that patent, by choosing a Walshfunction of order 8 provides 8 orthogonal codes in the presentembodiment using spread spectrum CDMA uses the all 0 Walsh sequence as apilot carrier with the other 7 sequences available for moving basestation communications. The code sequences may be repeated as ABCDEFG;ABCDEFG; . . . . Although fewer codes could be used, preferably no lessthan 3 are used. Because of differing propagation times for signalsbetween a particular moving base station and two or more different fixedradio ports, it is not possible to satisfy the condition of timealignment required for Walsh function orthogonality for 2 or more fixedradio ports at one time. For this purpose, two outer pseudonoise codesare used to provide discrimination between signals arriving at themoving base station from different fixed radio ports. The pseudonoisecode rate is preferably 4,864 kilobits per second. The sequence lengthfor the transmitted carrier signal is preferably 32,768 chips, asdescribed in U.S. Pat. No. 5,103,459. The outer pseudonoise codesmodulate the signal in quadrature phase shift keying.

The pilot signal will be transmitted in both directions, from the movingbase stations to the fixed radio ports and vice, versa. This is madepossible by the line of site fading characterized as Rician.

The pilot sequence will be long enough that a number of differentsequences can be generated by shifts in the basic sequence. Theseparation will be great enough to ensure that there is no interferencebetween pilot signals. Each moving base stations will use a differentoffset from a neighboring moving base station to provide signalseparation. Similarly, each fixed radio port will use a different offsetfrom a neighboring fixed radio port.

The FCC has allocated a 20 mhz of unlicensed spectrum, including a 10mhz band for voice products and a 10-mhz band for data products. Thus,one continuous 10-megahertz channel is available and time divisionmultiplex transmission is preferably used. The bit rate for bothdirections of transmission will be twice the frequency division duplexrate, introducing an overall delay of 500 microseconds and a processinggain of 9 decibels. In the time division duplex mode, the transmissiontimes and direction, forward and reverse between the mobile unit and themoving base station and between the moving base station and the fixedradio ports, are aligned. In one half of the time division, duplex cyclesignals are transmitted from the mobile unit to the moving base stationand, from there, to the fixed radio port. In the other half-cycle,signals are transmitted from the fixed radio port to the moving basestation and then to the mobile unit.

The two 15-mhz licensed spectrum bands (30 mhz) are preferably dividedinto three 5-megahertz channels in each direction, utilizing the samearchitecture as described earlier herein with respect to the 5-megahertzlicensed spectrum. In the 15-mhz licensed spectrum, each of the5-megahertz channels will support 14 traffic channels, for a total of 42traffic channels in each 15-mhz band. The air interface between themoving base station and the fixed radio port, as well as the signalstructure, can be modified and adapted to a variety of allocations ofspectrum and air interface standards.

In the present embodiment, as described earlier herein, 7 orthogonalcodes are available for communication between the fixed radio ports 50and the moving base stations 30, 40. As described earlier herein anddepicted in FIGS. 6 and 7, one 16 bit communication channel, channel 19,is set aside for control and identification bits. As depicted in FIG. 7,channel 19 may comprise 7 control bits and 9 identification bits. The 9identification bits provide 512 unique identification numbers. Using 7orthogonal codes and 512 identification numbers, 3,854 moving basestations can be uniquely identified. When the moving base stations areseparated by a spacing of 200 feet, the total distance of coverage usingthe 3,854 moving base stations is approximately 135 miles. FIG. 1 showsa portion of the system with moving base stations moving in oppositedirections along oppositely directed roadways and fixed radio ports withdual antennas. Vehicular traffic moving in opposite directions on thesame roadway are preferably served by moving base stations on oppositesides of the roadway. Where each roadway has only one-way traffic, thesystem is preferably disposed between the roadways. In one embodiment ofthe invention, depicted in FIG. 9, two separate loops 200, 205 aredisposed between two separate roadways 206, 208 with the traffic on theroadways indicated by the arrows 207 and 209. The loops 200 and 205comprise moving base stations 210 and 250, respectively. The basestations, in this embodiment, are moving in the direction indicated bythe arrows 201 and 202. Since, as a practical matter, the loops 200, 205are not of indefinite length, a plurality of loops may be required tocover a desired area. To avoid interruption in communications, the endsof the loops are preferably sufficiently close together, or overlapping,to provide an overlapping area of coverage for mobile units traveling inthe area of the loop ends. This will allow one of the mobile stationsnearing the end of the loop of which it is a part to hand off the callto a mobile station of the adjacent loop.

Each loop preferably has a single gateway for connection to the wiretelephone network. One advantage of that arrangement is that iteliminates the need for registration of moving base stations, which isrequired where a moving base station moves between gateways. FIG. 9shows a pair of gateways 215 associated with the loop 200 and a pair ofgateways 255 associated with the loop 205. The two gateways of a loopare both connected to the fixed radio ports of the loop at all times andmay be operated in a load sharing mode with each capable of handling thetotal telecommunication's traffic for the loop in the event of a failurein one of the gateways.

To avoid interrupting communications with a mobile unit traveling alongthe roadway in the area where two adjacent loops end, any existing callsare handed off from the moving base station near the terminating end ofits loop to a moving base station of the next loop. The handoff processis essentially the same as a handoff between moving base stations on thesame loop, except that the handed off call will be routed to the wirenetwork to a different gateway. This procedure is equivalent to ahandoff between cell sites of different cells in the existing cellularnetwork in a manner which is well known in the art. The loops 200 and205 may physically overlap to assure proper overlap of communicationsbetween moving base stations of the two loops and to avoid loss ofcommunication with a mobile unit handed off from one loop to another.

The timing and synchronization between the moving base station and afixed radio port with which the moving base station communicates isphase-locked to the pilot signals received from the fixed radio portwith which the moving base station communicates. For synchronizationpurposes, the moving base station will receive a Global PositioningSatellite (GPS) Coordinated Universal Time (UCT) timing signal once eachsecond.

CDMA Technology is well-known for sensitivity to power control.Specifically, the more powerful signals tend to “mask out” less powerfulsignals at the receiver. Typically, elaborate power control schemes areimplemented to ensure that all signals arrive at the receiver at thesame level. In accordance with the system of this invention, however,the sensitivity to power level of CDMA is used to advantage. Theprinciples of signal transmission employed in the system of theinvention is illustrated in FIG. 8. Two power levels of radiotransmission, high (H) and low (L), are defined. Referring to FIG. 1,high-power level signals are transmitted from the moving base station 30to the mobile unit 20 and from the base station 30 to the fixed radioport 50. Low power level signals are transmitted from the fixed radioport 50 to the moving base station 30. Similarly, low power signals aretransmitted from the mobile unit 20 to the moving base station 30. Sincethe moving base station receives a low power level signal from the fixedradio port and transmits a high level power signal toward terminals, thehigh power level received at the mobile unit 20 will mask out anysignals of the low power signal transmitted from the fixed radio port tothe moving base station. In a similar fashion, any low signaltransmitted from the mobile unit 20 reaching the fixed radio port 50will be masked by the high power level signal transmitted from themoving base station to the fixed radio port. As stated earlier, theantennas 100-105, 110, 111 are preferably highly directional antennaswith very little feedback from the transmit signal to the receivesignal. Feedback due to reflections and other extraneous sources can bereadily eliminated at the moving base station using well-known noisecancellation techniques.

When a mobile unit set is first powered up or first enters a servicearea, the mobile unit must register in the manner described earlier, bytransmitting its unique address in the new service area. The addresswill be received by the closest moving base station 30 and transmittedvia a fixed radio port and the gateway switch 60 to the telephonenetwork. This registration procedure is required so that an incomingcall for the mobile unit can be appropriately directed.

The spacing of mobile based stations 20 and the fixed radio ports 50 ofFIG. 1, together with the strength of the signal transmitted between themoving base stations and the fixed radio ports, determines the number offixed radio ports with which a moving base station can communicate atany point in time. The spacing and signal strength is preferably suchthat each fixed radio port receives signals from three moving basestations. When a fixed radio port receives data, accompanied by theidentification number of the moving base station, the processor 150(FIG. 2) computes a signal quality indication on the received signal.The signal quality indication is a figure of merit preferably computedas a function of signal strength and signal-to-noise ratio. It is addedto the received data and added to the fiber optic ring 55 via the ADM152. The gateway 60 preferably receives the same data from severaldifferent ones of the fixed radio ports 50 and stores the data in aninternal memory in the gateway 60 in association with the moving basestation identification number and Walsh function spreading code. Theaddress of the fixed radio port from which the data has been received isstored in the memory of processor 64 as well. Accordingly, multiplecopies of the same data transmitted by a single moving base station arestored in the memory of the processor 64 in the gateway. The signalquality indications computed by the processors 150 in each of severalfixed radio ports are compared to a predefined signal quality indicationthreshold, and the data corresponding to a signal quality indicationbelow the threshold value is discarded. Otherwise, the data is retained.A cyclic redundancy code transmitted with the data is used to detect anyTDM frame errors. The best data, i.e., associated with the best signalquality indication is transferred from the gateway 60 to the telephonenetwork. Data received from the telephone network at the gateway 60 andintended for a registered mobile unit is stored in the memory of theprocessor 150 in a register particularly associated with the moving basestation currently serving the mobile unit. This data will be sent viathe optical ring 55 to all fixed radio ports that are identified in thememory of the processor 65 as fixed radio ports with an acceptablesignal quality indication. The received data will be transmitted fromeach of the fixed radio ports which received the data together with theidentification code and Walsh function code of the moving base stationto which the data is directed. The transmission of data from differentfixed radio ports will be staggered, delayed by different amounts, sothat they can be received and separated at the moving base stations. Thedelays can be precisely controlled by means of synchronous distributionvia the optical ring 55, in the SONET or SDH format. The receivingmoving base station, by means of its processor 130, compares themultiple copies of the received data signals, aligns them and combinesthem for the best reception.

Each of the moving base stations will have one of N assigned codes,where N may be any number, but preferably is at least 3 or more. SevenWalsh function codes are preferably used. The codes may be repeated insequence, as for example, ABCDEFGABCDEFG. The codes are assigned insequence to the various moving base stations so that two moving basestations having the same code will be physically separated by asufficient distance to prevent interference in the communicationsbetween fixed radio ports and moving base stations having the sameidentity code. The operation of the fixed base stations 70 isessentially the same as that of a standard fixed base station. Incongested traffic areas, a mobile unit which is stopped or slowlymoving, e.g., less than 30 miles per hour, will preferably be servicedby one of the fixed base stations 70. As the speed of travel of themobile unit 20 increases, a handoff will occur between the fixed basestation and a moving base station. The procedures for determiningwhether a mobile unit is to be served by a fixed base station or amoving base station are the same procedures as described earlier hereinin determining which moving base station is selected to serve a mobileunit, i.e., based on signal strength and error rate. Thus, when a callinvolving a mobile unit is initiated or when it is determined that ahandoff should occur, the mobile unit may be handed from a movingstation to a fixed station, or vice versa. Each mobile unit monitorspilot signals from fixed and moving base stations and synchronizes tothe base station providing the best signal. The mobile unit may“connect” with three fixed or moving base stations while searching for afourth in what is known as the “soft” hand-off mode. As the speed of thevehicle increases, fixed or slow moving base stations will be dropped.In more congested areas where traffic speed will vary between 0 and 60miles per hour, base stations speed may, for example, be set to move at30 mph. The moving base station should then be able to accommodate alltraffic in the 0-60 mph range.

It will be understood that the above-described arrangement is merelyillustrative of the application of the principles of the invention andthat other arrangements may be devised by those skilled in the artwithout departing from the scope of the invention as defined by theappended claims.

What is claimed is:
 1. A system comprising: a plurality of base stationinterface circuits positioned on Earth and geographically distributed inaccordance with a path; a first plurality of spatially separatedantennas; a first receiver connected to the first plurality of spatiallyseparated antennas, the first receiver configured to receive, throughthe first plurality of spatially separated antennas, a plurality ofcellular signals transmitted from the plurality of base stationinterface circuits, each cellular signal of the plurality of cellularsignals including first data for a mobile device, a second plurality ofspatially separated antennas; a first transmitter connected to thesecond plurality of spatially separated antennas, the first transmitterconfigured to transmit, through the second plurality of spatiallyseparated antennas, the first data to the mobile device while the mobiledevice, the first receiver, and the first transmitter are moving in thesame direction relative to the plurality of base station interfacecircuits and along the path; a second receiver connected to the secondplurality of spatially separated antennas, the second receiverconfigured to receive, through the second plurality of spatiallyseparated antennas, second data from the mobile device; and a secondtransmitter connected to at least one of the first plurality ofspatially separated antennas, the second transmitter configured totransmit another cellular signal comprising the second data to at leastone base station radio interface circuit of the plurality of basestation interface circuits while the mobile device, the second receiver,and the second transmitter are moving in the same direction relative tothe plurality of base station interface circuits and along the path. 2.A system in accordance with claim 1, wherein each base station interfacecircuit is configured to transmit at least one of the plurality ofcellular signals.
 3. A system in accordance with claim 1, wherein theplurality of cellular signals and the another cellular signal comprisingthe second data are code division multiple access (CDMA) signals.
 4. Asystem in accordance with claim 1, wherein each base station interfacecircuit of the plurality of base station interface circuits is connectedto a sectorized antenna such that each base station interface circuit isconnected to a corresponding sectorized antenna, each cellular signal ofthe plurality of cellular signals transmitted from each base stationinterface circuit through the corresponding sectorized antenna.
 5. Asystem in accordance with claim 1, wherein each base station interfacecircuit of the plurality of base station interface circuits is connectedto a phased array antenna with directional radio frequency beams suchthat each base station interface circuit is connected to a correspondingphased array antenna, each cellular signal of the plurality of cellularsignals transmitted from each base station interface circuit through thecorresponding phased array antenna connected to the base stationinterface circuit.
 6. A system in accordance with claim 1, wherein thefirst plurality of spatially separated antennas is configured asdirectional antenna sectors.
 7. A system in accordance with claim 1,wherein the first plurality of spatially separated antennas isconfigured as a plurality of phased array antennas with directionalradio frequency beams.
 8. A system in accordance with claim 1, whereinthe second transmitter is configured to transmit the another cellularsignal comprising the second data to at least two of the plurality ofbase station radio interface circuits while the mobile device, thesecond receiver, and the second transmitter are moving relative to theplurality of base station interface circuits and along the path.
 9. Asystem comprising: a plurality of base station interface circuitspositioned on Earth in accordance with a path; a plurality of sectorizedantennas, each base station interface circuit connected to acorresponding sectorized antenna of the plurality of sectorizedantennas; a first plurality of spatially separated antennas; a firstreceiver connected to the first plurality of spatially separatedantennas, the first receiver configured to receive, through the firstplurality of spatially separated antennas, a plurality of code divisionmultiple access (CDMA) cellular signals transmitted from the pluralityof base station interface circuits, each CDMA cellular signal of theplurality of CDMA cellular signals including first data for a mobiledevice and transmitted from one of the plurality of base stationinterface circuits through the corresponding sectorized antenna; asecond plurality of spatially separated antennas; a first transmitterconnected to the second plurality of spatially separated antennas, thefirst transmitter configured to transmit, through the second pluralityof spatially antennas, the first data to the mobile device while themobile device, the first receiver, and the first transmitter are movingin the same direction relative to the plurality of base stationinterface circuits and along the path; a second receiver connected tothe second plurality of spatially separated antennas, the secondreceiver configured to receive, through the second plurality ofspatially separated antennas, second data from the mobile device; and asecond transmitter connected to at least one of the first plurality ofspatially separated antennas, the second transmitter configured totransmit a CDMA cellular signal comprising the second data to at leasttwo base station radio interface circuits of the plurality of basestation interface circuits while the mobile device, the second receiver,and the second transmitter are moving in the same direction relative tothe plurality of base station interface circuits and along the path. 10.A system in accordance with claim 9, wherein the first plurality ofspatially separated antennas is configured as directional antennasectors.
 11. A system in accordance with claim 9, wherein the firstplurality of spatially separated antennas is configured as a pluralityof phased array antennas with directional radio frequency beams.
 12. Asystem in accordance with claim 9, wherein the sectorized antennas arephased array antennas with directional radio frequency beams.
 13. Anapparatus comprising: a first plurality of spatially separated antennas;a second plurality of spatially separated antennas; a first receivermeans for receiving, through the first plurality of spatially separatedantennas, a plurality of code division multiple access (CDMA) cellularsignals from a plurality of base station interface circuits positionedon Earth and distributed in accordance with a path, each CDMA cellularsignal of the plurality of CDMA cellular signals comprising first datafor a first mobile device and second data for a second mobile device,the second data different from the first data; a first transmitter meansfor transmitting, through the second plurality of spatially separatedantennas, the first data to the first mobile device and the second datato the second mobile device while the first mobile device and the secondmobile device are moving along the path relative to the plurality ofbase station interface circuits and in a direction that is the same asthe direction that the apparatus is moving; a second receiver means forreceiving, through the second plurality of spatially separated antennas,third data from the first mobile device and fourth data from the secondmobile device, the fourth data different from the third data; and asecond transmitter means for transmitting another CDMA cellular signalcomprising the third data and the fourth data to at least one basestation radio interface circuit of the plurality of base stationinterface circuits, while the apparatus is moving relative to theplurality of base station interface circuits along the path.
 14. Theapparatus in accordance with claim 13, wherein the first transmittermeans is for transmitting the first data and the second data while theapparatus is on an overhead vehicle moving along the path relative tothe plurality of base station interface circuits.
 15. An apparatus inaccordance with claim 13, where the second transmitter means is fortransmitting the another CDMA cellular signal through at least one ofthe first plurality spatially separated of antennas.
 16. An apparatus inaccordance with claim 13, wherein the first plurality of spatiallyseparated antennas is configured as directional antenna sectors.
 17. Anapparatus in accordance with claim 13, wherein the first plurality ofspatially separated antennas is configured as a plurality of phasedarray antennas with directional radio frequency beams.
 18. An apparatusin accordance with claim 17, wherein the first plurality of spatiallyseparated antennas comprises antenna means for transmitting spatiallyseparated radio frequency beams separated in time with a predefined timedelay.
 19. An apparatus in accordance with claim 13, further comprisinga processor means for aligning and combining the plurality of CDMAcellular signals.
 20. An apparatus in accordance with claim 13, whereinthe second transmitter means is for transmitting the third data and thefourth data within time slots of time-division multiplex channels withinthe another CDMA cellular signal.